Cultivated Varieties of Native Plants

Monarda fistulosa 'Claire Grace'

As more and more people learn about native plants and their value in the home landscape, the concept of cultivars arises. My blogs have included mention of cultivars over the years as I recognize their value and availability in not just stores but also at native plant sales. I thought I’d write about some of the concerns with using them and mention some of the research that I’ve found.

Let’s set the definition of the term: “cultivar” means “cultivated variety.” In the plant world, it is a plant that someone created or found, recognized it as different (e.g., different flower or leaf color), and trademarked a name for it. Many people refer to native cultivars as “nativars” but—from a grammar point of view—that term is unnecessary. The word cultivar already reflects the concept perfectly so that is the word that I choose to use here.

Let me clarify that this post is not about hybrids. Hybrids are crosses of two different species (e.g., a cross of Lobelia cardinalis and Lobelia siphilitica). Hybrids are usually registered by the breeder and named in way to indicate the cross. Yes, desirable hybrids are sold as cultivars, but not all cultivars are hybrids.

Besides hybrids, cultivars can be a plant sport—also called a selection—found  in the wild or in a garden, that is recognized for a desired trait and then named and propagated to maintain that trait (usually by cuttings or tissue culture). It can also have been bred specially using different plants of the same species as parents. This latter definition is the type that I want to talk about and I’ll call this a “species cultivar.”

You can generally tell the difference between a hybrid and a species cultivar by the name (if it is properly shown): Lobelia ‘Ruby Slippers’ is a hybrid—note that no species name is given, only the genus (it might also be shown as Lobelia x ‘Ruby Slippers’); Asclepias tuberosa ‘Hello Yellow’ is a cultivar of a single species of milkweed. This milkweed cultivar fits my definition of “species cultivar.” 

Are your eyes glazed over yet? Well, keep going because, next, it’s important to understand how cultivars come to be selected. Those reasons affect how we consider them for our use. There are several reasons for selecting a plant to be a cultivar, including:

• Flower traits (double flowers, odd flower colors, fragrance, longer bloom time/repeat bloom)
• Leaf color (variegation, dark foliage, leaf markings)
• Leaf shape (deeply lobed, attractive edges)
• Plant form (weeping, dwarf, strong branching, spreading form)
• Fruit characteristics (larger berries, more nuts, fewer seeds)

Phlox paniculata 'Jeana' with one
flower of the species to compare size

'Jeana' is quite popular with butterflies;
 I have written about it here in my garden

As the number of advocates for using native plants increases (and yay for that!), the voices of people insisting that no cultivars be used has grown louder. While I recognize that using straight species (e.g., Asclepias tuberosa) has important value—and is essential for restoration—the discussion about using cultivars needs a broader understanding of the actual cultivar being considered. Some cultivars can be safely used to bring beauty and value to the landscape while still supporting bugs, butterflies, and birds just as well as straight species plants.  The factors that I would consider based on the known research so far:

• What is the cultivar’s change over the straight species? For example, does it have less pollen and nectar or dark-colored leaves? Or does it have a longer flowering period or a weeping form?
• How many of the cultivar will be used in the landscape compared to straight species? Using a mix of cultivar and straight species is preferable to using only the cultivar (to improve genetic diversity).
• Why is the cultivar being considered for use in this planting? Is it a showy landscape where natives would not be used if this cultivar couldn’t be used to add some star power? Would they use an exotic plant instead?
• Is this for a restoration project? Cultivars and even out of region straight species plants should not be used for restoration.

Recent research by Doug Tallamy and others focused on the question of how supportive cultivars are to native insects. Here is some of the information that I found.

From A Way to Garden’s podcast interview with Doug Tallamy in May 2018: “We just finished a study looking at six common cultivar traits in native plants, and seeing how they might have impacted insect use of that plant. Now these are all woody plants, so we did not look at flowering; we did not look at flowers at all. So we didn’t look at the impact on pollinators; other people are doing that. But just in terms of how well leaves support caterpillars and other things that drive food webs. We looked at what happens when you make a green leaf, red or purple. What happens when you change that leaf into a variegated form? What happens when you take a tall plant and make it short, or change the habit in some way? When you enhance fall color? When you increase fruit size? What was the other trait? I think that’s it; there were six traits. The only thing that consistently deterred insect feeding was taking a green leaf and making it red or purple.”

From Ecobeneficial’s podcast in October 2015: “Enhanced berry size is another feature Tallamy examined. With the “bigger is better” attitude now so prevalent, many cultivars are being selected for their enormous berries. Much to his surprise, the larger-berried Highbush Blueberry cultivars supported more insect species than their straight species counterparts.”

Research on how pollinators use the flowers is important too. From Annie White’s pollinator research on cultivars from 2013-2016:

“Some native cultivars attract just as many insect pollinators as the native species. This was seen mostly for open-pollinated seed cultivars such as Asclepias tuberosa ‘Hello Yellow’ and Monarda fistulosa ‘Claire Grace.’ One native cultivar selection, Veronicastrum virginicum ‘Lavendelturm’ actually attracted significantly more total pollinators than the native species and had a longer bloom time. This illustrates that there’s potential for pollinator-friendly cultivars (with long bloom periods and high nectar production) to be selected for and marketed.

One clear trend was observed across all species; the more manipulated the cultivars became, the less attractive they became to pollinators. Cultivars such as Achillea millefolium ‘Strawberry Seduction’ and Symphyotrichum novae-angliae ‘Alma Poetschke’, which are the result of repeated selections in breeding programs, attracted significantly fewer pollinators in nearly all pollinator groups.

If evaluating native cultivars for use in a pollinator habitat garden, try to limit the use of cultivars to open-pollinated seed-grown “selections” or “sports” of the native species. Cultivars that differ significantly in color and morphology from the native species should be used cautiously and cultivars with hybrid origins should be avoided in the context of pollinator habitat restoration.”

From The Humane Gardener, I found an interesting interview with the same Annie White; the interview gives an expanded explanation on her point about hybrids, using the Lobelia cardinalis x Lobelia siphilitica hybrids as an example. Read more here.  

So if the question asked is: Should we choose cultivars of native plants? The answer is “It depends.”

The considerations, again, that you should consider: 

1) If the plant has flower traits that reduce nectar and pollen, then NO; 

2) If the plant has dark leaf forms, then NO; 

3) If the plant has other modified traits such as form and fruit size, then probably OK; 

4) If the plant species are NOT regionally appropriate for your garden, then NO; 

5) If you will be planting some of the straight species as well for biodiversity, then probably OK. 

The bottom line is that we should know what we’re buying. If you want to buy a cultivar, it’s important to do the research to understand how well the plant will support local native partners like bees, butterflies, and birds (or accept that is not why you’re buying it). If one is not willing to do the research, then the best recommendation is to buy straight species.  

Clethra alnifolia 'Hummingbird'
cultivated for dwarf form

Clethra alnifolia 'Hummingbird'
always has summer pollinators